The new hybrid BBN model with the photon cooling, X particle, and the primordial magnetic field

Abstract

The Big Bang Nucleosynthesis theory accurately reproduces the abundances of light elements in the universes, except for the Li-7 abundance. The calculated Li-7 abundance with the baryon-to-photon ratio fixed by the observations of the cosmic microwave background (CMB) is inconsistent with the observed lithium abundances on the surface of metal-poor halo stars, and this problem is called "Li-7 problem". Previous studies proposed to resolve this Li-7 problem include photon cooling (possibly via the Bose-Einstein condensation of a scalar particle), the decay of a long-lived X particle (possibly the nextto-lightest supersymmetric particle), or an energy density of a primordial magnetic field (PMF). We review and analyze the results of these solutions both separately and in concert, and the constraint on the X particles and the PMF parameters from observed light-element abundances with a likelihood analysis. We can discover parameter ranges of the X particles which can solve the Li-7 problem and constrain the energy density of the PMF.